Supply independent Schmitt trigger RC oscillator

ABSTRACT

Embodiments of the present invention provide an oscillator circuit having a steady output frequency that is independent of the supplied voltage. This oscillator includes a Schmitt trigger circuit which may be implemented within an integrated circuit of a wireless terminal or other like portable electronic device. The Schmitt trigger circuit receives a threshold voltage input and a second voltage input. The Schmitt trigger circuit generates an output voltage equal to either a first output voltage or a second output voltage based on the results of comparing the threshold voltage input to the second voltage input. An RC network may be coupled to the output of the Schmitt trigger circuit and is operable to supply the second voltage input to the Schmitt trigger circuit. A voltage divider network also couples to the output of the Schmitt trigger circuit wherein the threshold voltage input is proportional to the first output voltage reduced by the voltage divider network based on the output voltage of the Schmitt trigger circuit.

CROSS REFERENCE TO RELATED PATENTS/PATENT APPLICATIONS ContinuationPriority Claim, 35 U.S.C. §120

The present U.S. Utility Patent Application claims priority pursuant to35 U.S.C. §120, as a continuation, to the following U.S. Utility PatentApplication which is hereby incorporated herein by reference in itsentirety and made part of the present U.S. Utility Patent Applicationfor all purposes:

1. U.S. Utility application Ser. No. 11/236,191, entitled “Supplyindependent Schmitt trigger RC oscillator,” filed Sep. 27, 2005,pending, and scheduled to issue as U.S. Pat. No. 7,529,317 on May 5,2009, which claims priority pursuant to 35 U.S.C. §119(e) to thefollowing U.S. Provisional Patent Application which is herebyincorporated herein by reference in its entirety and made part of thepresent U.S. Utility Patent Application for all purposes:

a. U.S. Provisional Application Ser. No. 60/720,576, entitled “Supplyindependent Schmitt trigger RC oscillator,” filed Sep. 26, 2005, nowexpired.

Incorporation by Reference

The following U.S. Provisional Patent Application is hereby incorporatedherein by reference in its entirety and is made part of the present U.S.Utility Patent Application for all purposes:

c. U.S. Provisional Application Ser. No. 60/603,148, entitled “Methodand system improving reception in wireless receivers throughredundancy,” filed Aug. 20, 2004, now expired.

BACKGROUND OF THE INVENTION

1. Technical Field of the Invention

The present invention relates generally to oscillators, and moreparticularly to the type of oscillator utilized in high frequency powerconverters where initial and final frequencies are required to be welldefined.

2. Description of Related Art

Cellular wireless communication systems support wireless communicationservices in many populated areas of the world. While cellular wirelesscommunication systems were initially constructed to service voicecommunications, they are now called upon to support data communicationsas well. The demand for data communication services has exploded withthe acceptance and widespread use of the Internet. While datacommunications have historically been serviced via wired connections,cellular wireless users now demand that their wireless units alsosupport data communications. Many wireless subscribers now expect to beable to “surf” the Internet, access their email, and perform other datacommunication activities using their cellular phones, wireless personaldata assistants, wirelessly linked notebook computers, and/or otherwireless devices. The demand for wireless communication system datacommunications will only increase with time. Thus, cellular wirelesscommunication systems are currently being created/modified to servicethese burgeoning data communication demands.

Cellular wireless networks include a “network infrastructure” thatwirelessly communicates with wireless terminals within a respectiveservice coverage area. The network infrastructure typically includes aplurality of base stations dispersed throughout the service coveragearea, each of which supports wireless communications within a respectivecell (or set of sectors). The base stations couple to base stationcontrollers (BSCs), with each BSC serving a plurality of base stations.Each BSC couples to a mobile switching center (MSC). Each BSC alsotypically directly or indirectly couples to the Internet.

In operation, each base station communicates with a plurality ofwireless terminals operating in its cell/sectors. A BSC coupled to thebase station routes voice communications between the MSC and a servingbase station. The MSC routes voice communications to another MSC or tothe PSTN. Typically, BSCs route data communications between a servicingbase station and a packet data network that may include or couple to theInternet. Transmissions from base stations to wireless terminals arereferred to as “forward link” transmissions while transmissions fromwireless terminals to base stations are referred to as “reverse link”transmissions. The volume of data transmitted on the forward linktypically exceeds the volume of data transmitted on the reverse link.Such is the case because data users typically issue commands to requestdata from data sources, e.g., web servers, and the web servers providethe data to the wireless terminals.

To conserve power, the wireless terminal may sleep when not activelycommunicating with a servicing base station. However, to ensure nocommunications are missed, the wireless terminal awakens periodically toreceive a page burst that indicates if the wireless terminal mustservice a communication from the servicing base station. Various otherelectronic devices may enter a sleep mode as well in order to conservepower. To realize this advantage, the timing associated with the sleepmode should be accurately controlled in order to allow the wirelesstelephone to awaken at predetermined intervals to check for receivedmessages or pages. Thus, it is important to have an accurate low poweroscillator for timing when to awaken from or enter into the sleep modeand effectively conserve power.

One such low power oscillator is a Schmitt trigger RC oscillator. FIG. 1depicts a general Schmitt trigger RC oscillator 10. Schmitt trigger RCoscillator 10 includes an operational amplifier 12 that receives a firstvoltage input or threshold voltage input V_(P) and a second voltageinput V_(N). Operational amplifier 12 generates an output voltage,V_(OUT), equal to a first output voltage, V_(DD), when V_(P) is greaterthan V_(N); or a second output voltage, such as ground, when V_(P) isless than V_(N). A resistive capacitive (RC) network 14 couples to theoutput of operational amplifier 12 and supplies V_(N) to operationalamplifier 12. Additionally a voltage divider 16 also couples to theoutput of operational amplifier 12. As shown here, V_(P) is suppliedfrom the voltage divider 16, as the voltage seen at the node betweenresistors R1 and R2.

When V_(P)>V_(N), V_(OUT) goes to V_(DD) and begins to charge capacitorC_(X). This increases the voltage V_(N). During this charging period,V_(P1)=V_(REF)+R₁/(R₁+R₂)*(V_(DD)−V_(REF)). When V_(N) exceeds theswitching point V_(P), V_(OUT) goes to ground and begins to dischargecapacitor C_(X). This decreases the voltage V_(N). During thisdischarging period, V_(P2)=R₂/(R₁+R₂)*V_(REF). Then, the switching pointdefined by V_(P) is a function of V_(DD) and V_(REF). During ChargingPeriod, V_(N) may be defined as

$V_{N} = {{{V_{DD}( {1 - {\mathbb{e}}^{\frac{- t_{1}}{R_{X}C_{X}}}} )} + {V_{P\; 2}( {\mathbb{e}}^{\frac{- t_{1}}{R_{X}C_{x}}} )}} = {V_{P\; 1}.}}$During the discharging period, V_(N) may be defined as

$V_{N} = {{V_{P\; 1}*{\mathbb{e}}^{\frac{- {({t_{2} - t_{1}})}}{R_{X}C_{X}}}} = {V_{P\; 2}.}}$Solving these two equations, where for example R₁=R₂, yields anexpression for the period of the oscillator be defined

${{as}\mspace{14mu} t_{2}} = {{- R_{X}}*C_{X}*{{\ln( {\frac{\frac{1}{2}( {V_{DD} - V_{REF}} )}{V_{DD} - {\frac{1}{2}V_{REF}}}*\frac{V_{REF}}{V_{DD} + V_{REF}}} )}.}}$Thus, the frequency of the oscillator may be defined as 1/t₂, which is afunction (R_(X), C_(X), V_(DD), V_(REF)).

The output of the operational amplifier may be a continuous square waveas shown in FIG. 2. The frequency of this square way depends on thevalues of R and C and the threshold points of the Schmitt trigger. TheSchmitt trigger RC oscillator circuit may be easily incorporated withinan integrated circuit (IC). However, it should be noted that thefrequency stability is lacking as the frequency is dependent on theinput voltage V_(DD) and V_(REF) for the reasons shown above. As theinput voltage can vary as much as +/−10 percent, the frequency may alsovary +/−10 percent. This level of variation makes the Schmitt triggeroscillator unacceptable as an accurate timing source for determiningwhen to awaken from or enter into the sleep mode and effectivelyconserve power.

BRIEF SUMMARY OF THE INVENTION

The present invention is directed to apparatus and methods of operationthat are further described in the following Brief Description of theSeveral Views of the Drawings, the Detailed Description of theInvention, and the claims. Other features and advantages of the presentinvention will become apparent from the following detailed descriptionof the invention made with reference to the accompanying drawings.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

FIG. 1 depicts a general Schmitt trigger RC oscillator;

FIG. 2 depicts the output of an operational amplifier;

FIG. 3 is a system diagram illustrating a portion of a cellular wirelesscommunication system that supports wireless terminals operatingaccording to the present invention;

FIG. 4 is a block diagram functionally illustrating a wireless terminalconstructed according to the present invention;

FIG. 5 is a block diagram illustrating in more detail the wirelessterminal of FIG. 4, with particular emphasis on the digital processingcomponents of the wireless terminal;

FIG. 6 is a block diagram illustrating the formation of paging channeldownlink transmissions;

FIG. 7 is a timeline illustrating the receipt and decoding of pagingbursts particularly comparing full decoding to partial decodingaccording to the present invention;

FIG. 8 depicts a general Schmitt trigger RC oscillator according to anembodiment of the present invention; and

FIG. 9 is a logic flow diagram illustrating one method of utilizing theSchmitt Trigger RC Oscillator of FIG. 8 according to an embodiment ofthe present invention.

DETAILED DESCRIPTION OF THE INVENTION

FIG. 3 is a system diagram illustrating a portion of a cellular wirelesscommunication system 100 that supports wireless terminals operatingaccording to the present invention. The cellular wireless communicationsystem 100 includes a Mobile Switching Center (MSC) 101, Serving GPRSSupport Node/Serving EDGE Support Node (SGSN/SESN) 102, base stationcontrollers (BSCs) 152 and 154, and base stations 103, 104, 105, and106. The SGSN/SESN 102 couples to the Internet 114 via a GPRS GatewaySupport Node (GGSN) 112. A conventional voice terminal 121 couples tothe PSTN 110. A Voice over Internet Protocol (VoIP) terminal 123 and apersonal computer 125 couple to the Internet 114. The MSC 101 couples tothe Public Switched Telephone Network (PSTN) 110.

Each of the base stations 103-106 services a cell/set of sectors withinwhich it supports wireless communications. Wireless links that includeboth forward link components and reverse link components supportwireless communications between the base stations and their servicedwireless terminals. These wireless links support digital datacommunications, VoIP communications, and other digital multimediacommunications. The cellular wireless communication system 100 may alsobe backward compatible in supporting analog operations as well. Thecellular wireless communication system 100 supports the Global Systemfor Mobile telecommunications (GSM) standard and also the Enhanced Datarates for GSM (or Global) Evolution (EDGE) extension thereof. Thecellular wireless communication system 100 may also support the GSMGeneral Packet Radio Service (GPRS) extension to GSM. However, thepresent invention is also applicable to other standards as well, e.g.,TDMA standards, CDMA standards, etc. In general, the teachings of thepresent invention apply to digital communications that combine AutomaticRepeat ReQuest (ARQ) operations at Layer 2, e.g., LINK/MAC layer withvariable coding/decoding operations at Layer 1 (PHY).

Wireless terminals 116, 118, 120, 122, 124, 126, 128, and 130 couple tothe cellular wireless communication system 100 via wireless links withthe base stations 103-106. As illustrated, wireless terminals mayinclude cellular telephones 116 and 118, laptop computers 120 and 122,desktop computers 124 and 126, and data terminals 128 and 130. However,the cellular wireless communication system 100 supports communicationswith other types of wireless terminals as well. As is generally known,devices such as laptop computers 120 and 122, desktop computers 124 and126, data terminals 128 and 130, and cellular telephones 116 and 118,are enabled to “surf” the Internet 114, transmit and receive datacommunications such as email, transmit and receive files, and to performother data operations. Many of these data operations have significantdownload data-rate requirements while the upload data-rate requirementsare not as severe. Some or all of the wireless terminals 116-130 aretherefore enabled to support the GPRS and/or EDGE operating standard aswell as supporting the voice servicing portions the GSM standard.

FIG. 4 is a block diagram functionally illustrating a wireless terminal200 constructed according to the present invention. The wirelessterminal 200 of FIG. 4 includes an RF transceiver 202, digitalprocessing components 204, and various other components contained withina housing. The digital processing components 204 includes two mainfunctional components, a physical layer processing, speech COder/DECoder(CODEC), and baseband CODEC functional block 206 and a protocolprocessing, man-machine interface functional block 208. A Digital SignalProcessor (DSP) is the major component of the physical layer processing,speech COder/DECoder (CODEC), and baseband CODEC functional block 206while a microprocessor, e.g., Reduced Instruction Set Computing (RISC)processor, is the major component of the protocol processing,man-machine interface functional block 208. The DSP may also be referredto as a Radio Interface Processor (RIP) while the RISC processor may bereferred to as a system processor. However, these naming conventions arenot to be taken as limiting the functions of these components.

The RF transceiver 202 couples to an antenna 203, to the digitalprocessing components 204, and also to a battery 224 that powers allcomponents of the wireless terminal 200. The physical layer processing,speech COder/DECoder (CODEC), and baseband CODEC functional block 206couples to the protocol processing, man-machine interface functionalblock 208 and to a coupled microphone 226 and speaker 228. The protocolprocessing, man-machine interface functional block 208 couples to aPersonal Computing/Data Terminal Equipment interface 210, a keypad 212,a Subscriber Identification Module (SIM) port 213, a camera 214, a flashRAM 216, an SRAM 218, a LCD 220, and LED(s) 222. The camera 214 and LCD220 may support either/both still pictures and moving pictures. Thus,the wireless terminal 200 of FIG. 4 supports video services as well asaudio services via the cellular network.

FIG. 5 is a block diagram illustrating in more detail the wirelessterminal of FIG. 4, with particular emphasis on the digital processingcomponents of the wireless terminal. The digital processing components204 include a system processor 302, a baseband processor 304, and aplurality of supporting components. The supporting components include anexternal memory interface 306, MMI drivers and I/F 308, a video I/F 310,an audio I/F 312, a voice band CODEC 314, auxiliary functions 316, atleast one clock or oscillator circuit 317, a modulator/demodulator 322,ROM 324, RAM 326 and a plurality of processing modules. In someembodiments, the modulator/demodulator 322 is not a separate structuralcomponent with these functions being performed internal to the basebandprocessor 304.

The processing modules are also referred to herein as accelerators,co-processors, processing modules, or otherwise, and include auxiliaryfunctions 316, an equalizer module 318, an encoder/decoder module 320,and an Incremental Redundancy (IR) processing module 328. Theinterconnections of FIG. 5 are one example of a manner in which thesecomponents may be interconnected. Other embodiments supportadditional/alternate couplings. Such coupling may be direct, indirect,and/or may be via one or more intermediary components.

RAM and ROM service both the system processor 302 and the basebandprocessor 304. Both the system processor 302 and the baseband processor304 may couple to shared RAM 326 and ROM 324, couple to separate RAM,coupled to separate ROM, couple to multiple RAM blocks, some shared,some not shared, or may be served in a differing manner by the memory.In one particular embodiment, the system processor 302 and the basebandprocessor 304 coupled to respective separate RAMs and ROMs and alsocouple to a shared RAM that services control and data transfers betweenthe devices. The processing modules 316, 318, 320, 322, and 328 maycoupled as illustrated in FIG. 5, but may also be coupled in othermanners in differing embodiments.

The system processor 302 services at least a portion of a servicedprotocol stack, e.g., GSM/GPRS/EDGE protocol stack. In particular thesystem processor 302 services Layer 1 (L1) operations 330, a portion ofIncremental Redundancy (IR) GSM protocol stack operations 332 (referredto as “IR control process”), Medium Access Control (MAC) operations 334,and Radio Link Control (RLC) operations 336. The baseband processor 304in combination with the modulator/demodulator 322, RF transceiver,equalizer module 318, and/or encoder/decoder module 320 service thePhysical Layer (PHY) operations performed by the digital processingcomponents 204.

A clock module or oscillator module 317 may service both the systemprocessor 302 and the baseband processor 304. This module may producetiming information which when accurate may be used to significantlyconserve battery power. For example, to conserve power, the wirelessterminal may sleep when not actively communicating with a servicing basestation. However, to ensure no communications are missed, the wirelessterminal awakens periodically to receive a page burst that indicates ifthe wireless terminal must service a communication from the servicingbase station. A description of this process will be described withreference to FIG. 6. Various other electronic devices known to thosehaving skill in the art may also enter a sleep mode as well in order toconserve power. To realize this advantage, the timing associated withthe sleep mode should be accurately controlled based on timing signalsproduced by oscillator module 317 in order to allow the wirelesstelephone to awaken at predetermined intervals to check for receivedmessages or pages.

FIG. 6 depicts the various stages associated with forming andinterpreting paging channel (PCH) downlink transmissions. The originalpages for the individual wireless terminals or mobile stations areinitially divided into a series of pages to be transmitted according toa predetermined schedule to the wireless terminals. This predeterminedschedule allows the individual wireless terminals, when not activelytransmitting, to enter a sleep mode and merely awaken when it isnecessary to receive their respective page bursts. As shown here, theoriginal page undergoes two stages of encoding. First, the originalpages undergo a block coding operation that is typically referred to asouter encoding. The block coding stage, allows for the detection oferrors within the data block. In addition, the Data blocks may besupplemented with tail bits or block code sequence. Since Block Codingis the first or external stage of channel coding, the block code is alsoknown as an external or outer encoding scheme. Typically, two kinds ofcodes are used, a cyclic redundancy check (CRC) or a Fire Code. The FireCodes allow for either error correction or error detection. Errordetection with the Fire Code, verifies connectivity.

Next, the pages undergo a second level of encoding that typically is aconvolutional coding referred to as inner encoding. The pages may beoptionally interleaved to form paging bursts. These paging bursts arewhat the wireless terminal receives according to the predeterminedschedule.

FIG. 7 is a timeline illustrating the receipt and decoding of pagingbursts particularly comparing full decoding to partial decodingaccording to the present invention. Illustrated in FIG. 7 are a seriesof paging bursts 400 that are received according to paging groupsreceived approximately every 0.5 to 2.0 seconds. The paging bursts carryeither a page or a null page for each wireless terminal assigned to acorresponding paging group. When carrying a page, the paging burst 400signal the wireless terminal to respond to the servicing base station.This may involve servicing a voice call, data or text. When the pagingburst 400 is sent, individual wireless terminals that are assigned tothe paging group awaken for a period of time indicated by the awakeportion of timeline 402 to receive the paging burst.

Typically, 4 paging bursts makeup every paging message and traditionallyall 4 paging bursts need to be received before decoding can begin. Bymaking use of the Null page template a sufficiently reliable indicationof whether or not the paging message contains any useful information forthe mobile can be obtained from only the 1st paging burst of the 4paging bursts without waiting the 4 paging bursts. If after receivingthe 1st paging burst and performing the null pattern match the result isinconclusive then the 2nd paging burst can be received and tested forconformity to the null paging message, and so on until all 4 bursts havebeen received. As one can appreciate, each paging burst which does nothave to be received over the air-interface provides measurable anduseful power consumption benefits. If all 4 paging bursts of the blockare received and decoded, this constitutes normal paging messagereception/decoding. The benefits result from reducing the time that theradio (RF) portion of the receiver is employed (receiving 1 or 2 burstsinstead of 4 bursts) and bypassing a large amount of unnecessarybaseband message decoding and further processing to understand thecontents of the message.

Timeline 402 shows that the wireless terminal's processors are eitherawake or asleep. When the wireless terminal awakens it may fully decodethe paging burst. Alternatively, according to the present invention,when there is a favorable pattern comparison between the paging burstand a null page pattern, the wireless terminal determines that thepaging burst is a null page. However, one should note that a null pagemight be required to be fully decoded. Time segments 404 and 406 showthat the time required to fully decode the paging burst is much greaterthan that required to merely perform a pattern comparison on theprocessed paging burst with an existing pattern. Therefore one canappreciate that the wireless terminal will remain awake much longer whena full decode of the paging burst is required. This means thatadditional power will be consumed and processing resources will beutilized to fully decode the paging burst when compared to merelyconducting a pattern comparison as indicated in block 406.

FIG. 8 depicts a general Schmitt trigger RC oscillator 800. Schmitttrigger RC oscillator 800, like Schmitt trigger RC oscillator 10 of FIG.1 includes an operational amplifier 12 that receives a first voltageinput or threshold voltage input, V_(P), and a second voltage input,V_(N). Operational amplifier 12 generates an output voltage, V_(OUT),equal to a first output voltage, V_(DD), when V_(P) is greater thanV_(N); or a second output voltage, such as ground, when V_(P) is lessthan V_(N). However, as shown here, a defined relationship existsbetween V_(P) and V_(DD). Resistive capacitive (RC) network 14 couplesto the output of operational amplifier 12 and supplies V_(N) tooperational amplifier 12. Additionally a voltage divider 16 also couplesto the output of operational amplifier 12. The relationship betweenV_(P) and V_(DD) is defined by the values of the resistances of thevoltage divider 16. As shown here, V_(P) is supplied from the voltagedivider 16, as the voltage seen at the node between resistors R1 and R2.

In order to simplify analysis, one can assume R₁=R₂=R₃. WhenV_(P)>V_(N), V_(OUT) goes to V_(DD) and begins to charge capacitorC_(X). This increases the voltage V_(N). During this charging period,V_(P1)=(⅔)*V_(DD). When V_(N) exceeds the switching point V_(P), V_(OUT)goes to ground and begins to discharge capacitor C_(X). This decreasesthe voltage V_(N). During this discharging period, V_(P2)=(⅓)*V_(DD).Thus, the switching point, V_(P), is no longer defined as a function ofV_(REF). Rather, the switching point is a predetermined portion ofV_(DD). During Charging Period, V_(N) may be defined as

$V_{N} = {{{V_{DD}( {1 - {\mathbb{e}}^{\frac{- t_{1}}{R_{X}C_{X}}}} )} + {\frac{1}{3}{V_{DD}( {\mathbb{e}}^{\frac{- t_{1}}{R_{X}C_{x}}} )}}} = {\frac{2}{3}{V_{DD}.}}}$During the discharging period, V_(N) may be defined as

$V_{N} = {{\frac{2}{3}V_{DD}*{\mathbb{e}}^{\frac{- {({t_{2} - t_{1}})}}{R_{X}C_{X}}}} = {\frac{1}{3}{V_{DD}.}}}$Solving these two equations, where R₁=R₂=R₃, yields an expression forthe period of the oscillator be defined as t₂=2 ln(2*R_(X)C_(X)). Thus,the frequency of the oscillator may be defined as 1/t₂, which is afunction Rx and Cx.

The output of the operational amplifier may be a continuous square waveas previously described with reference to FIG. 2. The frequency of thissquare way depends only on the values of R_(X) and C_(X) as thedependence on the threshold points of the Schmitt trigger and referencevoltage have been canceled out by replacing the reference with groundand making the threshold points a function of V_(DD). The Schmitttrigger RC oscillator circuit may be easily incorporated within anintegrated circuit (IC) such as that containing or coupled to oscillatormodule 317 that may service both the system processor 302 and thebaseband processor 304. This oscillator provides greater frequencystability as the frequency is not dependent on the input voltage V_(DD)for the reasons shown above. As the input voltage can vary as much as+/−10 percent, the possibility of frequency variations is reduced oreliminated. This reduced level of variation makes this Schmitt triggerRC oscillator an acceptable and accurate timing source for determiningwhen to awaken from or enter into the sleep mode and effectivelyconserve power.

FIG. 9 is a logic flow diagram illustrating one method of utilizing theSchmitt Trigger RC Oscillator, for which one embodiment is described inFIG. 8, in order to provide a timing signal having a steady frequencywithin a portable electronic device such as a wireless terminal.Beginning with Step 802, the portable electronic device, such as but notlimited to a wireless terminal, enters a sleep mode for a sleep period.The Schmitt Trigger RC Oscillator circuit is used to monitor theduration of the sleep mode in Step 804. Because the Schmitt Trigger RCOscillator Circuit is a lower power oscillator, battery power of theportable electronic device is able to be conserved. Additionally, byeliminating the frequency variations as seen when comparing the SchmittTrigger RC Oscillator circuits of FIG. 1 and FIG. 8, a more accuratedetermination of the time to awaken the portable electronic device maybe determined such that in Step 806 the portable electronic device maybe awakened from the sleep mode in order to receive an encoded pagingburst. Previous timing inaccuracies would have decreased the actual timespent in the sleep mode or required higher power oscillator circuits tobe employed. This burst is processed in Step 808. A comparison of theresults of processing the encoded paging burst are made with a null pagepattern, or other like means, to determine whether or not the encodedpaging burst received is a null page. At Decision Point 812, when thecomparison made to determine whether or not the received encoded pagingburst corresponds to a null page pattern is favorable, the process maycontinue to Step 814 wherein the portable electronic device is able toenter or reenter the sleep mode. In this way additional battery powermay be conserved during the next sleep mode. However, if the comparisonis unfavorable at Decision Point 812, it may be necessary to fullyawaken the portable electronic device in order to respond to thepage/service call at Step 816.

In summary, embodiments of the present invention provide an oscillatorcircuit having a steady output frequency that is independent of thesupplied voltage. This oscillator includes a Schmitt trigger circuitwhich may be implemented within an integrated circuit of a wirelessterminal or other like portable electronic device. The Schmitt triggercircuit receives a threshold voltage input and a second voltage input.The Schmitt trigger circuit generates an output voltage equal to eithera first output voltage or a second output voltage based on the resultsof comparing the threshold voltage input to the second voltage input. AnRC network may be coupled to the output of the Schmitt trigger circuitand is operable to supply the second voltage input to the Schmitttrigger circuit. A voltage divider network also couples to the output ofthe Schmitt trigger circuit wherein the threshold voltage input isproportional to the first output voltage reduced by the voltage dividernetwork based on the output voltage of the Schmitt trigger circuit.

Additional embodiments may employ the Schmitt trigger RC oscillatorcircuit within portable electronic devices or devices where it isdesirable to conserve power, such as a wireless terminal, such that alow power oscillator circuit may be used to provide a steady frequencytiming signal for the purpose of determining when to awaken from andenter into a sleep mode in order to conserve power.

As one of average skill in the art will appreciate, the term“substantially” or “approximately”, as may be used herein, provides anindustry-accepted tolerance to its corresponding term. Such anindustry-accepted tolerance ranges from less than one percent to twentypercent and corresponds to, but is not limited to, component values,integrated circuit process variations, temperature variations, rise andfall times, and/or thermal noise. As one of average skill in the artwill further appreciate, the term “operably coupled”, as may be usedherein, includes direct coupling and indirect coupling via anothercomponent, element, circuit, or module where, for indirect coupling, theintervening component, element, circuit, or module does not modify theinformation of a signal but may adjust its current level, voltage level,and/or power level. As one of average skill in the art will alsoappreciate, inferred coupling (i.e., where one element is coupled toanother element by inference) includes direct and indirect couplingbetween two elements in the same manner as “operably coupled”. As one ofaverage skill in the art will further appreciate, the term “comparesfavorably”, as may be used herein, indicates that a comparison betweentwo or more elements, items, signals, etc., provides a desiredrelationship. For example, when the desired relationship is that signal1 has a greater magnitude than signal 2, a favorable comparison may beachieved when the magnitude of signal 1 is greater than that of signal 2or when the magnitude of signal 2 is less than that of signal 1.

The foregoing description of a preferred embodiment of the invention hasbeen presented for purposes of illustration and description. It is notintended to be exhaustive or to limit the invention to the precise formdisclosed, and modifications and variations are possible in light of theabove teachings or may be acquired from practice of the invention. Theembodiment was chosen and described in order to explain the principlesof the invention and its practical application to enable one skilled inthe art to utilize the invention in various embodiments and with variousmodifications as are suited to the particular use contemplated. It isintended that the scope of the invention be defined by the claimsappended hereto, and their equivalents.

1. A method for operating a communication device, the method comprising:based on a timing signal generated by a Schmitt resistive-capacitive(RC) oscillator circuit, awakening the communication device from a sleepmode period to receive an encoded paging burst; processing the encodedpaging burst to determine if the encoded paging burst is a null page;based on a determination of the encoded paging burst being a null page,entering the communication device into at least one additional sleepmode period; and based on a determination of the encoded paging burstnot being a null page, employing the communication device to processfully the encoded paging burst.
 2. The method of claim 1, wherein theSchmitt RC oscillator circuit includes: an amplifier circuit thatreceives a first input voltage and a second input voltage, wherein theamplifier circuit is operative to generate an output voltage equal to: afirst output voltage when the first input voltage is greater than thesecond input voltage; and a second output voltage when the first inputvoltage is less than the second input voltage; a groundedresistive-capacitive (RC) network, coupled to the output voltage, thatis operative to supply the second input voltage to the amplifiercircuit; and a voltage divider network, coupled to the output voltage,wherein the first input voltage is proportional to the first outputvoltage as determined by the voltage divider network.
 3. The method ofclaim 2, wherein: the first output voltage is a power supply voltage;and the second output voltage is ground.
 4. The method of claim 2,wherein: the voltage divider network includes: a first resistor having afirst end coupled to the output voltage and having a second end coupledto a second resistor; the second resistor having a first end coupled tothe first resistor and having a second end that is grounded; and a thirdresistor having a first end coupled to the first end of the secondresistor and the second end of the first resistor and first resistor andhaving a second end that is coupled to a power supply voltage.
 5. Themethod of claim 1, wherein: the Schmitt RC oscillator circuit isimplemented within an integrated circuit of the communication device. 6.The method of claim 1, further comprising: performing pattern comparisonof the encoded paging burst with a predetermined pattern to determine ifthe encoded paging burst is a null page.
 7. The method of claim 6,wherein: the pattern comparison performs less than a full decoding ofthe encoded paging burst.
 8. The method of claim 6, wherein: a firsttime period during which pattern comparison is performed is relativelyless than a second time period during which the communication deviceprocesses the encoded paging burst.
 9. The method of claim 1, furthercomprising: after the communication device processes the encoded pagingburst, entering the communication device into at least one additionalsleep mode period.
 10. The method of claim 1, wherein: the communicationdevice is a wireless communication device.
 11. An apparatus, comprising:a clock module, implemented using a Schmitt resistive-capacitive (RC)oscillator circuit, that is operative to generate a timing signal; abaseband processor module, coupled to the clock module, that isconfigured to: awaken from a sleep mode period based on the timingsignal; and process an encoded paging burst to determine if the encodedpaging burst is a null page; and wherein: based on a determination ofthe encoded paging burst being a null page, the apparatus enters into atleast one additional sleep mode period; and based on a determination ofthe encoded paging burst not being a null page, the baseband processormodule fully processes the encoded paging burst.
 12. The apparatus ofclaim 11, further comprising: a modulator/demodulator module, coupled tothe baseband processor module, that is operative to demodulate areceived signal thereby generating the encoded paging burst.
 13. Theapparatus of claim 11, wherein the Schmitt RC oscillator circuitincludes: an amplifier circuit that receives a first input voltage and asecond input voltage, wherein the amplifier circuit is operative togenerate an output voltage equal to: a first output voltage when thefirst input voltage is greater than the second input voltage; and asecond output voltage when the first input voltage is less than thesecond input voltage; a grounded resistive-capacitive (RC) network,coupled to the output voltage, that is operative to supply the secondinput voltage to the amplifier circuit; and a voltage divider network,coupled to the output voltage, wherein the first input voltage isproportional to the first output voltage as determined by the voltagedivider network.
 14. The apparatus of claim 11, wherein: the firstoutput voltage is a power supply voltage; and the second output voltageis ground.
 15. The apparatus of claim 11, wherein: the basebandprocessor module is operative to perform pattern comparison of theencoded paging burst with a predetermined pattern to determine if theencoded paging burst is a null page.
 16. The apparatus of claim 15,wherein: a first time period during which pattern comparison isperformed is relatively less than a second time period during which thebaseband processor module fully processes the encoded paging burst. 17.The apparatus of claim 11, wherein: the apparatus is a wirelesscommunication device.
 18. An apparatus, comprising: amodulator/demodulator module that is operative to demodulate a receivedsignal thereby generating an encoded paging burst; a clock module,implemented using a Schmitt resistive-capacitive (RC) oscillatorcircuit, that is operative to generate a timing signal; a basebandprocessor module, coupled to the clock module and to themodulator/demodulator module, that is configured to: awaken from a sleepmode period based on the timing signal; and process the encoded pagingburst to determine if the encoded paging burst is a null page; andwherein: based on a determination of the encoded paging burst being anull page, the apparatus enters into at least one additional sleep modeperiod; based on a determination of the encoded paging burst not being anull page, the baseband processor module fully processes the encodedpaging burst; the baseband processor module is operative to performpattern comparison of the encoded paging burst with a predeterminedpattern to determine if the encoded paging burst is a null page; and afirst time period during which pattern comparison is performed isrelatively less than a second time period during which the basebandprocessor module fully processes the encoded paging burst.
 19. Theapparatus of claim 18, wherein the Schmitt RC oscillator circuitincludes: an amplifier circuit that receives a first input voltage and asecond input voltage, wherein the amplifier circuit is operative togenerate an output voltage equal to: a first output voltage when thefirst input voltage is greater than the second input voltage; and asecond output voltage when the first input voltage is less than thesecond input voltage; a grounded resistive-capacitive (RC) network,coupled to the output voltage, that is operative to supply the secondinput voltage to the amplifier circuit; and a voltage divider network,coupled to the output voltage, wherein the first input voltage isproportional to the first output voltage as determined by the voltagedivider network.
 20. The apparatus of claim 18, wherein: the apparatusis a wireless communication device.